Three new natural cyclopentenedione derivatives from Piper carniconnectivum

A New Cytotoxic Tetrahydroxanthene-1,3(2H)-dione Derivative from Uvaria cordata and Structure Revision of Valderramenol A

A new tetrahydroxanthene-1,3(2H)-dione derivative (1) was isolated from the leaves of Uvaria cordata collected in Viet Nam. Its structure was elucidated to be a mixture of four tautomers (1a–1d) by a combination of extensive spectroscopic analyses and the theoretical calculation of Gibbs free energies. Compound 1 exhibited moderate cytotoxicity against KB, LNCaP, Hep-G2, MKN-7, SW-480, HL-60, and SK-Mel-2 cancer cell lines with IC50 values ranging from 25.92 ± 2.33 to 44.29 ± 4.36 μg/mL. In addition, the previously reported structure of valderramenol A has been revised to 1a/1b.

Cytotoxic non-aromatic B-ring flavanones from Piper carniconnectivum C. DC

The EtOAc extract from the leaves of Piper carniconnectivum C. DC. was subjected to chromatographic separation to afford two non-aromatic B-ring flavanone compounds: 5-hydroxy-2-(1'-hydroxy-4'-oxo-cyclohex-2'-en-1'-yl)-6,7-dimethoxy-2,3-dihydro-4H-chromen-4-one (1) and 5-hydroxy-2-(1',2'-dihydroxy-4'-oxo-cyclohexyl)-6,7-dimethoxy-2,3-dihydro-4H-chromen-4-one (2). The absolute configuration of (+)-1 was unambiguously determined as 2S,1'R by electronic circular dichroism (ECD) spectroscopy and comparison to simulated spectra that were calculated using time-dependent density functional theory (TDDFT). This methodology allowed the assignment of the absolute configuration of (+)-2 also as 2S,1'R, except for the stereogenic center at C-2', which was assigned as R because of the evidence drawn from high resolution NMR experiments. The cytotoxic activity of both compounds and 3 (hydrogenated B-ring derivative of 1) was evaluated on twelve human leukemia cell lines, and the IC50 values (<10 μM) indicated the activity of 1 against seven cell lines.

Nostotrebin 6, a bis(cyclopentenedione) with cholinesterase inhibitory activity isolated from Nostoc sp. str. Lukesová 27/97

Nostotrebin 6, a new polyphenolic compound with a fully substituted 2,2'-bis(cyclopent-4-en-1,3-dione) skeleton, was isolated from a methanolic extract of the cyanobacterial strain Nostoc sp. str. Lukesová 27/97. The structure of this compound was determined using X-ray crystallography and further supported by NMR, IR spectroscopy, and MS. Nostotrebin 6 is an S-parabolic I-parabolic noncompetitive inhibitor of acetylcholinesterase (IC(50) = 5.5 microM) and an S-parabolic I-parabolic mixed inhibitor of butyrylcholinesterase (IC(50) = 6.1-7.5 microM). The inhibitory potency of nostotrebin 6 was compared with that of tacrine and galanthamine.